The microbial community coalescence describes the mixing of microbial communities and the merging of their surrounding environments. Despite its prevalence in natural ecosystems and its potential influence on ecological processes, little research focused on the extent of coalescence between aquatic microbial communities. In this research, we analyzed the microbial communities in the Three Gorges Reservoir, a typical deep-water reservoir on the Yangtze River. The biogeography and the coalescence of microbial communities in water and sediment were illustrated and analyzed based on 16S rRNA gene amplicon sequence variants (ASVs). Differences in composition and diversity were identified between microbial communities in water and sediment, and microbial communities in sediment were more diverse than those in water. Between adjacent communities, by calculating the proportion of overlapped taxa, adopting the SourceTracker algorithm, and quantifying the connectivity of microbial cohesion, we found that the extent of intra-medium coalescence was strong (19.8%) and inter-media coalescence was faint (0.2%). 50 keystone species were selected using the cohesion metric. They displayed a stronger coalescence extent than average, and formed an accumulating pattern from upstream to downstream in the Three Gorges Reservoir, exhibiting their importance in the ecological network. Potential influencing factors of microbial community coalescence in aquatic environments were discussed, including environmental conditions, types of habitats, suspended particles in water, and microscale microbial activities. To summarize, this research depicted the coalescence of microbial communities in a deep-water reservoir and emphasized its ecological importance. We anticipate more attention and further research on the processes of microbial coalescence in the aquatic environment, which might provide new insights into turnover of microbial keystone species and changes in aquatic ecological conditions.

微生物群落聚结描述了微生物群落的混合及其周围环境的融合。尽管它在自然生态系统中普遍存在并对生态过程产生潜在影响，但很少有研究关注水生微生物群落之间的聚结程度。在这项研究中，我们分析了长江上典型的深水水库三峡水库的微生物群落。基于 16S rRNA 基因扩增子序列变体 (ASV) 说明和分析了水和沉积物中微生物群落的生物地理学和聚结。确定了水和沉积物中微生物群落的组成和多样性差异，沉积物中的微生物群落比水中的微生物群落更多样化。相邻社区之间，通过计算重叠分类群的比例，采用SourceTracker算法，量化微生物内聚力的连通性，我们发现介质内聚结程度强（19.8%），介质间聚结程度弱（0.2%）。使用内聚度量选择了 50 个关键物种。它们在三峡水库中表现出比平均水平更强的聚结程度，并在三峡水库中形成了从上游到下游的聚集格局，显示了它们在生态网络中的重要性。讨论了水生环境中微生物群落聚结的潜在影响因素，包括环境条件、栖息地类型、水中悬浮颗粒和微尺度微生物活动。总结一下，这项研究描述了深水水库中微生物群落的融合，并强调了其生态重要性。我们期待对水生环境中微生物聚结过程的更多关注和进一步研究，这可能为微生物关键物种的更替和水生生态条件的变化提供新的见解。